WATCH: Nepal Earthquake Triggers Mount Everest Avalanche

Mountain climbing always carries with it certain risks. Climbing Mount Everest carries a particular risk. But this week climbers at the famed Everest base camp faced a disaster they probably did not expect when an earthquake hit Nepal triggering a Mount Everest avalanche.

At least 18 climbers were killed as a result of the recent 7.9 magnitude earthquake in Nepal, including at least three Americans, according to the U.S. State Department. The horrifying moments are captured on the video above. Sean Wisedale, a climber on the mountain at the time, described the experience in a blog post:

Mountains and glaciers shook all around us. It was terrifying. From the neighbouring mountain Pumori an avalanche was triggered. A massive ice slab sheared and thundered into Base Camp. It lifted rocks and boulders ahead of it, slamming into hundreds of tents in the center of the camp and spilling over onto the Khumbu glacier on the other side.

Among the mountain climbers who lost their lives was a medic and physician’s assistant from New Jersey, Marisa Eve Girawong, who worked for the Seattle-based guide service Madison Mountaineering. Tom Taplin, a filmmaker and photographer from Colorado who was making a documentary about the Mount Everest base camp, and a veteran Google executive, Dan Fredinburg who was climbing with three other Google employees were also among those killed.

More than 60 people were evacuated from the mountain on Sunday. Three helicopters ferried the climbers – two at a time – down to the base camp. Numerous climbers may now be cut off on routes leading to the summit of the world’s highest peak.

Rescue operations on the mountain were halted due to bad weather on Monday after 20 climbers were evacuated and 11 bodies retrieved, seven of them Nepalise and the rest foreign climbers. As many as 200 climbers were still stranded on Monday, and feared to be injured, running low on food and heat, and waiting for helicopter rescue hampered by poor weather conditions.

The stranded climbers are primarily at Base Camp #2, some 21,000 feet above sea level, and cut off by massive drifts, boulders and blocks of ice sent down the mountain during the quake and a series of aftershocks. What had formerly been a well-worn trail is now impassable. The make up of the Everest climb will forever be changed.

At least 4,000 people are feared dead throughout Nepal as a result of the 7.9 magnitude quake, making it the worst disaster to hit Nepal since a similar quake in 1934 when 8,500 people were killed.